Autonomous downhole tools used in subterranean wells are frequently programmed using a surface system computer prior to being integrated into a tool string and sent downhole. The surface system can initiate processes in the tool, for example the initiation of a countdown, in which operations of the tools begin after a time delay. However, communication between the surface system and the tool is often not possible during a period of time prior to integration and until after the tool is lowered into the hole. Certain tools, such as tubing conveyed, slick-line, logging while drilling (LWD), and measurement while drilling (MWD) tools may not have a wired connection to the surface system and can only be communicated to through mud pulse telemetry, which may not be possible until the tool is sufficiently integrated into the downhole tool assembly. In some cases, no communication between the surface system and the tool is possible during the entire job while the tool is integrated in the downhole assembly.
Once the programming is initiated, tools that do not have a connection to the surface may be expected to run autonomously for a duration of the job or for the entire job. At times it is desirable to have one or more processes within the tool start at a specified time prior to integrating the tool into the tool string without the use of a surface system. For instance, the surface system may be located far from the area of tool string integration, yet it is not desirable to initiate a process in the tool until the tool has been moved into the integration area. Furthermore, the time between removing the tool from the surface system and integrating the tool into the tool string may not be known in advance. In cases where the initiation of a process in a tool begins a countdown, it is desirable to be able to initiate the process at a chosen time prior to tool string integration.
Initiating a process within a downhole tool often involves using a power source, such as a surface system computer. Often, weather conditions and/or the safety risks associated with certain oil field rig zone areas, such as Zone 2 rig environments, can make the use of electric power sources dangerous. In such cases, it is desirable to initiate a process in a downhole tool without the use of electrical power.
When downhole tools are initiated using a surface system, it can be difficult to determine whether initiation was successful. Some tools produce a faint sound or vibration to indicate that a process has been initiated, which indications may be difficult for workers to detect in muddy, rainy, and/or noisy oil field environments.
A need exists for a simple means of initiating a process in an autonomous downhole tool that addresses the issues discussed above.